This invention relates to water treatment and is particularly concerned to provide a means of purifying water in an apparatus suitable for use in a post-mix beverage dispenser, although it will be appreciated that water treated according to the invention may be used for other purposes.
Water quality and purity vary considerably from location to location and it is an object of the invention to provide a means whereby the water to be used in a post-mix dispenser or for other use can be rendered of the desired quality and purity using a relatively simple to operate and renewable means.
To be suitable for use in beverages water should not have excessive bicarbonate, carbonate and organic matter. Chlorine and heavy metals may also need to be removed.
It is also an object of the invention to provide an improved water treatment device in which blockage of water flow through the device by the necessary precipitation of the unwanted impurities can be ameliorated.
It is known from U.S. Pat. No. 4,844,796 to provide a water treatment apparatus for post-mix beverage dispensers in which the water to be treated is passed into a removable disposable cartridge having a first, reactor section and a second, filter section wherein the water is heated in the reactor section firstly by passing through a heat exchanger and secondly by means of a heater. The heater is positioned in a central aperture defined by an annular portion of the cartridge whereby it does not come into direct contact with the water.
A similar heater arrangement is disclosed in U.S. Pat. No. 5,858,248 where the heater can be located in the central cavity of a disposable cartridge of a water treatment device. Alternative heater arrangements disclosed in this application are to position the heater around the outer cylindrical surface of the cartridge or to have a gas cylinder heater beneath a central xe2x80x9cchimneyxe2x80x9d, i.e. the central cavity defined by the annular portion of the cartridge.
In all these heater embodiments, the beater is kept separated from the water under treatment. It does not become covered in deposits of the precipitated impurities that come out of solution in the water during the heating and sieving stages that take place in the cartridge. Thus the heaters are reusable and not disposed of with the disposable cartridges.
We have now surprisingly found that an efficient and economic water purification means may be achieved without the need to separate the heater from the water under treatment and hence without the need for the heater to have a long built-in life expectancy.
Accordingly, in one aspect the invention provides a water treatment apparatus comprising a treatment housing having an inlet for the water to be treated, an outlet for the treated water, a heater within the housing to come into direct contact with the water and a filter between the heater and the outlet, and means to fill the housing with water up to a maximum level which leaves a headspace between the water and the roof of the housing, the entrance to the outlet being below the operating water level.
Preferably the inlet is arranged so that the water travels upwardly within the housing.
Conveniently, the housing is in the form of a disposable cartridge which may be dispensed with, including its heater, when its life expectancy is reached.
The cartridge may contain one or more perforated screens or meshes between the beater and the filter but this is not essential.
Thus in one preferred embodiment the apparatus comprises a cylindrical housing having an inlet for the water to be treated, a heater spaced above the base of the housing and, extending within the cylindrical housing, one or more perforated screen(s) above the heater, a filter above the screen(s) and an outlet for the treated water above the filter. The outlet may conveniently be through the closed upper end of the cylinder.
The outlet extends beneath the level of the water so that hot water leaves the treatment housing without going through the headspace. Steam and volatiles collect in the headspace and may be allowed to escape through a pressure relief valve, as is described in more detail below.
The unfiltered water, e.g. from the mains, may first pass through a heat exchanger to warm it before it passes into the housing. Treated heated water leaving the housing may be passed in the opposite direction through the heat exchanger to act as the heat exchange medium to warm the incoming mains water. The treated water is, thereby, conveniently cooled before being passed to a reservoir or for direct use.
In another preferred embodiment the heat exchanger and the water treatment housing may be contained in a single unit, preferably with the heat exchanger directly beneath the water treatment housing. This may be a unitary structure or two separate units, water treatment housing and heat exchanger, which may be completely or partially disposable. For example, the water treatment housing may be a disposable cartridge and the heat exchanger non-disposable.
This single unit arrangement has the advantage that pipework between the heat exchanger and the water treatment housing can be considerably reduced, if not eliminated. The heated water from the heat exchanger may pass directly into the water treatment housing and the treated water from the housing can pass directly back to the coils of the heat exchanger in order to heat the incoming water. This arrangement reduces the regions where precipitation deposits may build up and harmfully affect water flow. Also, with the heat exchanger directly below the water treatment housing, the inlet to the water treatment housing can readily enter at its cooler, lower end.
The inlet for the water to be treated may conveniently enter through the floor of the treatment housing but this is not essential. For example, in some embodiments the water to be treated may enter the housing through a pipe entering the housing through or near the roof, which pipe extends downwardly inside the housing towards its base. On leaving the pipe water, once the hosing is filled to the lower end of the pipe, will then travel upwardly.
In another aspect the invention provides a water treatment apparatus comprising a treatment housing and a heat exchanger, the treatment housing having an inlet for the water to be treated, an outlet for the treated water, a heater within the housing and a filter between the heater and the outlets the inlet to the treatment housing receiving water that has passed from a source of untreated water through the heat exchanger and the outlet from the treatment housing passing treated water back through the heat exchanger, and a bypass valve to close the heat exchanger to incoming untreated water and to allow the incoming untreated water to flow directly into the treatment housing, whereby the hot treated water passing through the heat exchanger sterilises the heat exchanger.
The bypass valve means may conveniently be a first valve on the inlet pipe to the heat exchanger which is open during normal operation to allow inflow of untreated water, e.g. mains water, and a bypass valve in a bypass pipe between the source of untreated water and the first valve. The bypass valve is closed during normal operation. In sterilisation mode, the first valve is closed and the bypass valve is opened, thereby allowing water into the bypass pipe which takes the untreated water directly into the treatment housing inlet.
This sterilisation arrangement may be used with side by side separate units, or single units, which may be used one above the other as described above, and with housings having heaters which may or may not be in direct contact with a the water.
Where the water treatment housing and the heat exchanger are housed side by side rather than one beneath the other, their upper ends may conveniently be closed by an appropriately shaped and gasketted single plate, e.g. of steel. The necessary pipework for the required water flows into and out of the two housings can then pass through appropriately sized and gasketted holes in the plate. However, in another embodiment this closure plate is replaced by a double skinned cover plate formed in two parts, preferably by injection moulding of plastics material. Integral galleries are moulded inside the plate to provide the necessary flow passages. Thus much of the external pipework into and out of the two housings can be eliminated and replaced by large-section integrally moulded passageways that are less likely to become blocked by deposits. Moreover, the double skinned plate can readily be opened, and stripped and cleaned more easily.
We have surprisingly found that the direct contact of the heater and the water it is heating does not harmfully affect the efficiency of the treatment process. Deposits, largely of calcium carbonate, form on the heater surface but they only build up to a degree and then break off and fall to the floor of the container. Moreover, we have found that deposits also build up around the interior wall or walls of the housing and also a xe2x80x9croofxe2x80x9d of deposits can build up on the lower surface of the lowermost screen or the lower surface of the filter when no screen is used. The water being treated, therefore, once this build up has occurred is in effect treated in an inner housing formed by accumulated deposits on the floor of the housing, an annular build up of deposits on the walls and the xe2x80x9croofxe2x80x9d formed of deposits. The deposit build up is sufficiently porous not to impede flow to any significant extent and the xe2x80x9croofxe2x80x9d may indeed act as a further filtration medium. Sufficient turbulence may be created during the treatment process to ensure that the build up of deposits on the heater breaks off from time to time so that the beating efficiency of the heater is not unduly impaired. The wattage density of the heater may be chosen, e.g. between 20 and 30 watts/cm2, to give sufficient power density to cause the deposits to bake, crack and fall off before any substantial thickness of deposit is formed. Alternatively, it may be found advantageous occasionally to take steps to break off these deposits on the heater. For example, the heater may be switched off and then given a burst of power. This xe2x80x9cburstxe2x80x9d could conveniently be applied, say, overnight when the water treatment is out of use so that break off of deposits may occur when the apparatus is brought into use the next day.
In other embodiments ultrasonic or other vibration, e.g. caused by AC mains frequency, of the heater may be used, if necessary, to break the deposits on the heater. The heater surfaces may also be polished or coated with low-friction material in order to assist breaking off of the deposits.
It will be appreciated that the wattage capacity of the heater will vary according to the volume and, particularly, to the through put of the water treatment housing. For example, a heater of from 1000 to 1200 watts can usefully be employed for a throughput of 12 to 18 liters per hour, i.e. the input of water into the treatment housing.
Conveniently, once the water treatment housing has initially filled up with water to the maximum desired level, the outlet may be retained in the open position for continuous flow, subject to a satisfactory water temperature having been reached and maintained, which is monitored by a temperature probe, e.g. a thermistor, and the inlet may be opened and closed as required to replenish the housing, the need for replenishment being detected by one or more water depth probes in the upper part of the housing. Thus the water depth probe or probes are used to trigger the switching on or off of water flow as required, e.g. through a valve and pressure regulator from a mains water supply.
As the water level, therefore, never goes above the maximum level defined by that water depth probe, the required headspace is provided between the water and roof of the housing. The headspace, as indicated above, receives steam from the heated water and this may include unwanted volatiles from the water.
In a more preferred embodiment the probes are fitted within a separate chamber within the housing, which chamber only receives treated water after it has passed through the heating stage, any screens and the filter. Such an arrangement is described in our co-pending International patent application no. PCT/GB99/03509 and has the advantage that the probes are not rendered inoperative by gradual calcification.
The water depth probes and/or additional probes may also be used to measure and monitor water quality, for example the ionised condition of the treated water. This may conveniently be done by measurement, for example, of the difference in conductivity or capacitance between the untreated and the treated water.
In a typical prior art water treatment device for post-mix beverages, water at ambient temperature, say about 10xc2x0 C., from the mains may be heated to about 90xc2x0 C. in the heat exchanger, passed to the water treatment housing where it is heated to about 115xc2x0 C. and then cooled in the heat exchanger to about 20xc2x0 to 30xc2x0 C. If desired, the water treatment apparatus of the present invention may be operated at similar water temperatures.
However, we have found that considerable deposits of impurities, particularly calcium carbonate, can build up in regions of the apparatus where they can harmfully affect performance, when such temperatures are used. For example, as the temperature of the incoming water heats up on its passage through the heat exchanger, deposits build up in the heat exchanger and these deposits can be significant in the final quarter of the heat exchanger passageways, where the water temperature is at its highest. The pipework leading from the heat exchanger to the water treatment housing area can also become badly xe2x80x9cfurredxe2x80x9d, thereby reducing its diameter. Of course, this latter problem can be ameliorated as suggested above by building the heat exchanger and water treatment housing as a unit. It is also possible to increase the diameter of the pipes and/or to use insulated pipes or internal surface polishing or non-stick coating.
We have, however, found that these unwanted deposits can be reduced, so that greater deposition can take place in the intended deposition regions, if the water temperature is constrained within different limits. For example, instead of heating the water to 90xc2x0 C. in the heat exchanger, it may be heated only to about 70xc2x0 to 75xc2x0 C. and passed into the water treatment housing at that lower temperature. It is then heated by the heater to about 115xc2x0 C. as usual but then is cooled, e.g. by a coil and fan arrangement to, for example 75xc2x0 to 85xc2x0 C., say 80xc2x0 C., before passing back through the heat exchanger. Deposits in the heat exchanger and in the pipework can thereby be greatly reduced.
Where more than one perforated screen or mesh are used, they may be of the same or different perforation sizes. For example, they may have apertures from 1 to 2 per inch. The perforated screens may have depending legs protruding downwardly from their undersides whereby the build up of deposits may take a corrugated form, thereby increasing the surface area of deposit and thereby prolonging the life of the unit by delaying the time when the build up is sufficient to harm performance.
The filter may be of any suitable material. We have found that cellular sponge-like plastics material, e.g. reticulated polyester based polyurethane foam, is particularly useful.
The water treatment housing is preferably fitted with a pressure relief valve which may operate, for example, at about 0.7 bar. Steam containing unwanted volatiles from the water passes from the headspace through the relief valve and may be cooled in a condenser tube before being allowed to drain away. For example the evaporation rate through this valve over a period of use of the apparatus may be of the order of 2% by weight of the water being treated. Preferably the pressure relief valve is a dead-weight relief valve of the type well known in the art.
Treated water from the apparatus of the invention will normally be passed to a reservoir, e.g. a bag in a box type reservoir, where it can cool before being drawn off for use. Moreover, the presence of a reservoir between the water treatment housing and the facility in which the treated water is to be used ensures that the facility cannot overdraw or suck treated water directly out of the treatment housing and thereby harmfully reduce the necessary operating pressure therein. In another preferred embodiment, therefore, the reservoir is provided with separate inlet and outlet pipes and the entry to the outlet pipe within the reservoir is positioned to be remote from the exit end of the inlet pipe within the reservoir. This also helps to prevent regions of xe2x80x9cstaticxe2x80x9d water sitting within the reservoir and not being drawn off which improves water hygiene, particularly for drinks dispensers. In this embodiment, the inlet and outlet pipes may be separately connected into the reservoir or they may form part of a single connector provided that their exit and entry positions respectively are remote from each other as described above.
When the treated water reservoir becomes fill, water flow through the apparatus is stopped, preferably by automatic control means, and the heater may be controlled to allow the heated water temperature to drop to, say, about 90xc2x0 C., i.e. the water is maintained at a lower temperature in a standby mode, so that when flow to the reservoir is again needed, the response time for the water to reach full treatment temperature is relatively fast.
The apparatus of the invention may conveniently be provided with a safety-first service function whereby it may be opened for servicing and cleaning. The apparatus may be housed in a cabinet, the door to which is closed by a controlled bolt operation, e.g. by a solenoid operated by a control board. The control board may be programmed whereby the solenoid cannot release the bolt until the water temperature within the apparatus has fallen to a predetermined level, e.g. 50xc2x0 C. When the control board is appropriately activated, e.g. by the pressing of a xe2x80x9cservicexe2x80x9d button, the following actions may then be automatically carried out. The outlet for treated water from the water treatment housing is closed and the heater is switched off. The inlet, e.g. for mains water into the apparatus is opened or maintained open if already open. Mains or other supply water floods through the apparatus as the supply water is regulated to a pressure above the operating pressure within the water treatment housing. As the housing outlet for treated water is closed, the incoming water forces hot water already in the apparatus out through the pressure relief valve. Mains water is passed into the apparatus until an internal temperature sensor e.g. thermistor probe, indicates that the desired cooler temperature has been reached. The control board then actuates the switching off of the water supply and instructs the solenoid to release the bolt to allow the cabinet door to be opened. After servicing and closure of the cabinet door, the solenoid lock on the bolt is re-set. This service function can allow servicing access much more quickly e.g. within a few minutes, compared with allowing the apparatus to cool normally. By way of example only, if the water treatment housing and the heat exchanger together hold six liters of water, passage of about 8 liters of cold mains water can reduce the temperature to 50xc2x0 C. in six to eight minutes.
In yet another embodiment, the efficiency of the heat exchanger may be improved by allowing a proportion of the untreated water leaving its-outlet to be drawn off, e.g. to drain away, rather than it all passing into the water treatment housing. Thus more cold water, e.g. from the mains, needs to be passed into the heat exchanger to achieve the same throughput, thereby resulting in an increased cooling effect on the treated water passing back and through the beat exchanger. This effect may be sufficient to eliminate the need for the coil and fan cooling arrangement described above for the cooling of the treated water before it enters the heat exchanger for cooling.